Phased array antennas exhibit desirable properties for communications and radar systems, the most salient of which is the lack of any requirement for mechanically steering the transmission beam. This feature allows for very rapid beam scanning and the ability to bring high power to a target or a receiver while minimizing typical microwave power losses. The basis for directivity control in a phased array antenna systems is wave interference. By providing a large number of sources of radiation, such as a large number of equally spaced antenna elements fed from a combination of in phase currents, high directivity can be achieved. With multiple antenna elements configured as an array, it is therefore possible, with a fixed amount of power, to greatly reinforce radiation in a desired direction.
FIG. 1 depicts a conventional multi phased array antenna system having multiple microwave radiating horns 33 connected to a respective transmission system. The antenna radiator 33 transmits a pattern which has a mainbeam and a series of lobes focused at differing solid angles which contribute to transmitting radio frequencies in a given direction. The term RF employed herein is considered particularly with respect to the "millimeter-wave" region of the RF spectrum (frequencies above 20 GHz). By modifying the phase angle of the RF signal representing the electric field, a phased array antenna system can both transmit and receive electromagnetic radiation from different angles. Typical phased array systems transmit and receive at frequencies selected from a frequency band in the range of between 300 Megahertz to 40 Gigahertz.
New applications for phased array antenna systems constantly push the design envelope for increasingly higher transmission frequencies, however, increasing the frequency requires that the radiating elements and the components associated with the radiating elements be placed in increasingly closer and closer proximity to one another. It is found that as the frequency of transmission increases, the use of multibeam arrayed configurations of antenna system elements becomes limited by the physical space required to incorporate the system elements.
Multibeam phased arrays are typically comprised of a multiplicity of individual beam forming transmission elements. The phased arrays are processed by combining the voltages from a plurality of beam forming signals that are individually phased, amplified, filtered and impressed on antenna elements, such as the radiator horns 33 of the prior art system of FIG. 1, to produce multiple beams in different directions. As shown, an RF beam 10-1, having a primary frequency f.sub.1 is connected to a transmitting power divider 20-1, whose multiple outputs 24-1 through 24-n are connected to separate phase shift means 25. The outputs of the phase shift means 25 for different beams are combined in a combiner means 22, whose function is to combine properly phased signals for each beam which are assigned to particular radiating elements.
A second RF beam 10-2 of another frequency f.sub.2 is connected through similar circuit elements as RF beam 10-1 as shown in the prior art system of FIG. 1. Thus, typically the radio frequency beam phase and amplitude ultimately to be transmitted by the antenna are first delivered to the beam forming network that consists of a plurality of multiplexed power dividers such as divider 20 which provides a plurality of signals and couples a signal having a particular phase to one input of a multiplicity of inputs of a plurality of combiners such as combiner 22. Essentially each combiner receives signals at each transmission frequency, with appropriate phase angles from each of the plurality of power dividers, and combines these inputs to form a composite signal for the transmitted RF energy. In the prior art as shown in FIG. 1, the combined RF signals are coupled to the transmitting elements through power amplifiers 26, filters 30 and finally the radiator horns 33.
The use of phased array antenna systems that have a high degree of fidelity across all the radiators 33 is crucial to the success of most applications to which phased array systems are employed. This is accomplished through use advanced technologies in antenna design and processing circuitry. For example, phased array antennas constructed from MMIC chip technology at each antenna subsystem element(forming the so-called active array antenna) allow for very large effective-radiated-power levels and large system redundancy. As newer technologies emerge it becomes feasible to extend the transmission frequencies into the tens of gigahertz. However, existing fabrication and electronic designs do not permit the close proximity of elements required at such newer higher frequencies. For example, an 8-beam phased array having 100 elements in the array would require eight 100-way power dividers, 800 phase shifters, and 100 eight-way combiners, plus 100 power amplifiers, filters and radiating elements. So large a number of components in the aggregate cannot feasibly be accommodated in the small space required in and about the antenna section of the conventional system, especially with the myriad of waveguides required for the many interconnections.
Phased array antennas are extremely expensive to produce, in part, because of the large number of interconnections for the signal distribution and phase control. The problems of system cost are compounded in multibeam phased array applications. As transmission frequencies for multibeam phased array systems are pushed to new limits, new and novel electronic design techniques must follow. The present invention provides a system that allows increases in the frequency of transmission of a multibeam RF transmission antenna system without being limited by physical space requirements.